Australian news, and some related international items

How bushfires generate their own weather

Why Victoria’s bushfires generated their own lightning, The Age , By Liam Mannix, March 4, 2019 —There are few sights more terrifying for a firefighter: a vast, dark storm cloud brewing above a bushfire, shooting out lightning.

On Sunday, the Licola bushfire east of Melbourne burned with such intensity it generated a huge thundercloud that fired hundreds of lightning strikes at nearby forests.

The Bunyip fire, which is believed to have wiped at least one town off the map, also generated its own weather system which fed the fire with extreme winds.

“It’s absolutely terrifying. And it’s dangerous as well, because that lightning can start new fires before the main fire,” says Dean Narramore, a meteorologist at the Bureau of Meteorology’s extreme weather desk.

How bushfires generate their own weather

As a bushfire burns, it generates hot, smoke-filled air.

This air is hotter than surrounding air and rapidly rises, forming a smoke plume.

As the plume rises, atmospheric pressure falls. This causes the plume to spread out, generating a “mushroom” on top of the plume.

The smoke plume is filled with moisture which is released by burning trees. The higher you go in the atmosphere, the cooler it gets, so the top parts of the plume get chilled.

This causes the moisture in the plume to condense (turn from water vapour into tiny water droplets) and form a cloud.

As the plume rises rapidly into the sky, cool air is sucked in to replace it. This causes extreme winds near the firefront. To fight a fire, you need to know which way it is burning. But when a fire-cloud forms and starts generating strong and unpredictable winds, the fire can become chaotic.